title: Brain activity associated with placebo suppression of the urge-to-cough in humans.
abstract: BACKGROUND
  Antitussive therapies are accompanied by a substantial placebo effect, indicating that inhibitory circuits in the brain have a significant capacity to regulate cough neural processing. However, essentially nothing is known about the identity of these inhibitory circuits or how they reduce coughing. Understanding these processes may help develop more effective antitussive therapies in the future.
  
  
  OBJECTIVE
  To identify regional changes in human brain activity related to the urge-to-cough after placebo antitussive administration.
  
  
  METHODS
  Seventeen healthy participants undertook functional magnetic resonance imaging while completing a series of inhalations of capsaicin to induce the urge-to-cough. The resultant brain responses associated with capsaicin inhalation without any treatment were compared with those induced by capsaicin after placebo antitussive administration.
  
  
  RESULTS
  There was a significant decrease in participants' ratings of urge-to-cough after the placebo antitussive administration. Brain activity associated with capsaicin inhalation was less in the somatosensory, primary motor, insula, and cingulate cortices during placebo antitussive trials compared with no treatment control subjects. By contrast, placebo trials were associated with increased activation in the prefrontal and left parietal cortices.
  
  
  CONCLUSIONS
  Placebo-related decreases in urge-to-cough are accompanied by commensurate decreases in several brain regions activated during capsaicin inhalation, suggesting that beliefs about treatment can modify the central processing of inputs arising from the airways. The prefrontal cortex and posterior parietal cortex are likely to play an active role in the modification of airway sensory processing after administration of a placebo.
authors.affiliation: 1 School of Biomedical Sciences, University of Queensland, St Lucia, Australia; and.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Leech
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Mazzone
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Farrell
mesh_terms: D000293:Adolescent; D000328:Adult; D000996:Antitussive Agents / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects* / Q000502:physiology; D001931:Brain Mapping; D002211:Capsaicin; D003371:Cough / Q000139:chemically induced / Q000188:drug therapy* / Q000503:physiopathology; D005260:Female; D059907:Functional Neuroimaging; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D015990:Placebo Effect; D010919:Placebos / Q000494:pharmacology*; D018689:Sensory System Agents; D055815:Young Adult
chemical_list: D000996:Antitussive Agents; D010919:Placebos; D018689:Sensory System Agents; D002211:Capsaicin